To quote Grandpa Simpson, "Everything everyone just said is either obvious or wrong".

Pointing out that "complex systems" have "layers of defense" is neither insightful nor useful, it's obvious. Saying that any and all failures in a given complex system lack a root cause is wrong.

Cook uses a lot of words to say not much at all. There's no concrete advise to be taken from How Complex Systems Fail, nothing to change. There's no casualty procedure or post-mortem investigation which would change a single letter of a single word in response to it. It's hot air.